Digital Hardware

Introduction to Digital Hardware Design

Introduction

    In the modern world, machines rely heavily on control and functionality, both of which are fundamentally enabled by electricity. From simple electronic devices to complex computing systems, every machine around us operates through carefully designed electronic components working together.

 When we look closer inside these machines, we find a large number of Integrated circuit (ICs). These chips are responsible for decision-making, control, data storage, and computation. their core, they are built from electronic circuits composed of various components such as transistors, resistors, and capacitors, along with their interconnections, that use mathematical rules and logical principles to represent and process information.

For many digital hardware products, it is also necessary to design and build some logic circuits from scratch. To implement these circuits, three main types of chips may be used : standard chips, programmable logic devices, and custom chips. These are discussed in this blog.

Before defining each type, it is important to understand why one approach is chosen over another. Hardware design is not arbitrary; design decisions are governed by several key factors While many considerations exist, the following are the principal factors that influence these choices:

• Reconfigurability: You can change the chip's function by reprogramming it. This makes it easy to update your design or fix mistakes. (I want to buy a component that I can change its behavior to do what I am saying to do even if I change my mind in the future or I want it to be with me for ever at any time and in any environment and allow me to make any function or perform any task that I want)
• Flexibility: You can use the same chip for many different projects.
• Rapid Prototyping: You can test ideas quickly. For exp, you might design an answering machine or a traffic light system, then program and test you chips right away. This helps you learn, fix and improve your design fast.
• Low Power Use: Many chips consume little power, so you can use them in portable devices.

1. Standard chips:

Numerous chips are available that implement some commonly-used logic circuits ( such as adders, subtractors, And Nor gates etc and other advanced ones). We call them Standard Chips because they usually conform to an agreed-upon standard in terms of functionality and physical configuration. Each standard chip contains a small amount of circuitry (usually involving fewer than 100 transistors) and performs a simple function. To build a logic circuit, the designer chooses the chips that perform whatever functions are needed and then defines how these chips should be interconnected to realize a large logic circuit. So they occupy too much space on printed circuit board (PCBss) and keep in mind that only part of a chip may be used not all of the functionality by relying on their design so there is component that are not used this leads to higher power consumption. Standard chips were popular for building logic circuits until the early 1980s nowadays we see them just in a few school as part of learning the basic implementation of older computational system. However, as integrated circuit technology improved, this approach became inefficient.

 

2. Programmable Logic Device (PLD)

In contrast to standard chips that have fixed functionality, it is possible to construct chips that contain circuitry which can be configured by the user to implement a wide range of different logic circuits. These chips have a very general structure and include a collection of programmable switches that allow the internal circuitry in the chips to be configured in many different ways. The designer can implement whatever functions are required for a particular application by setting the programmable switches as needed. The switches are programmed by the end user, rather than when the chip is manufactured. Such chips are known as programmable logic devices (PLDs). PLDs are available in a wide range of sizes, and can be used to implement very large logic circuits. The most commonly used type of PLD is known as a field-programmable gate array (FPGA). The largest FPGAs contain billions of transistors, and support the implementation of complex digital systems. An FPGA consists of a large number of small logic circuit elements, which can be connected together by using programmable swithces in the FPGA. Because of their high capacity, and their capability to be tailored to meet the requirements of a specific application, FPGAs are widely used. In summary, you do not get a fixed function at the factory. You set up the chip after you get it. You can reprogram the chip if you want to change its function using VHDL or Verilog. PLDs also include other types such as : 

• PLA (Programmable Logic Array)
• PAL (Programmable Array logic)
• GALs (Generic Array Logic devices)
• CPLDs (Complex Programmable Logic Devices)
• FPGAs (Field-Programmable Gate Array) 

3. Custom-Designed Chips

FPGAs are available as off-the-shelf components that can be purchased from different suppliers. Because they are programmable, they can be used to implement most logic circuits found in digital hardware. However, they also have a drawback in that the programmable switches consume chip area and limit the speed of operation of implemented circuits. Thus, in some cases, FPGAs may not meet the desired performance or cost objectives. In such situations it is possible to design a chip from scratch; namely, the logic circuitry that must be included on the chip is designed first and then the chip is manufactured by a company that has fabrication facilities. This approach is known as custom or semi-custom design, and such chips are often called Application-Specific Integrated Circuits (ASICs). The main advantage of a custom chip is that its design can be optimized over the total number of chips fabricated, may be lower than the total cost of off-the-shelf chips that would be needed to implement the same function(s). Moreover, if a single chip can be used instead of multiple chips to achieve the same goal, then less area is needed on a PCB that houses the chips in the final product. This results in a further reduction in cost. 

Application Specific Integrated Circuit (ASIC) Design Flow

Design Flow

Design Entry: In this phase, the microarchitecture is developed using hardware description languages such as VHDL, Verilog, and SystemVerilog.

Logic Synthesis: This phase involves creating a netlist that outlines the logic cells, their interconnections, and other necessary components, all derived from the HDL code.

System Partitioning: Here, the large die is divided into manageable ASIC-sized sections for more efficient design and implementation.

Pre-Layout Simulation: A simulation is conducted at this stage to identify and rectify any errors in the design.

Floor Planning: This step involves determining the exact locations of cells within each block.

Routing: In this phase, physical connections between blocks and cells are established.

Extraction: This stage is focused on assessing the electrical characteristics, such as resistance and capacitance, of the connections.

Post-Layout Simulation: This final simulation tests the entire system's functionality, including the impact of interconnect loads, before the design is sent for manufacturing.

Advantages of ASICs

we find major factors such as high performance, lower power consumption, smaller size, reduced cost per unit, higher security and fewer components. 

Applications of ASICs

The distinct characteristics of ASICs have transformed electronic manufacturing, leading to smaller die sizes and greater logic gate density per chip. Typically chosen for advanced applications, ASIC chips serve as IP cores in satellites, are crucial for ROM production, and are utilized in microcontrollers, as well as in a wide array of medical and research applications. Currently, one of the most notable uses of ASIC technology is in Bitcoin mining.

How do ASICs differ from FPGAs ? 

see the table bellow for a comparision:

Feature	FPGA	ASIC
Flexibility	High (reprogrammable)	Low (not reprogrammable)
Performance	Lower than ASIC	Higher performance for specific tasks
Power Consumption	Higher compared to ASIC	Lower (optimized for efficiency)
Development Cost	Low (no NRE cost)	High (high NRE cost)
Production Cost per Unit	Higher compared to ASIC	Lower (cost-effective at high volume)
Time to Market	Shorter (reprogrammable, adaptable)	Longer (due to design and fabrication)
Reprogrammability	Yes (can change algorithms post-production)	No (fixed design)
Suitable Production Cycle	Small to medium scale	High volume (to offset NRE costs)
Design Cycle	Shorter	Longer

Fun Fact: In the programmable chips if a chip in a system is destroyed or burned out you will never know its functionality even with reverse engineering simply because it is destroyed so if the designer never provide a documentation or a diagram for it it is hard to understand and restore it back it is not like standard chips that from its unique identifier you can identify the functionality and logic design of the chip.

Last updated: 2025-12-14